Method and apparatus for controlling spiral concentrators



Feb. l5, 1966 L, G, HENDRICKSON 3,235,079

METHOD AND APPARATUS FOR CONTROLLING SPIRAL CONGENTRATORS Filed July lo, 1962 FIG: 1 r r 1 RECORDER PULP @ENS/TY sP/RAL FEED n/srR/BUTER LolvrRoLL-RJ METER la] I /b` /6c /6d- 26 25 6 /4 6 /40 /4b /4 l J sP/RAL sP/RAL sP/RAL sP/RAL /5-` l c@ f c c? c d? C@ I K f I 24 k r r V f 2]/- T/L r k SPL/NER L V*- Pos/r/on/ER SPL/"ER 22 D/Lur/ON 4 23 W4 TER co/vcE/VTRNE sr-PASSED NEW FEED ro FEED [/9 20 y VALVE n WATER |r P03 "ONE" VALVE CONCHA/TRATE v ro PRooucr 1 {'L'V; /7 0R FURTHER L ISENSER ANU )Q J PUMP B0X /0 PROCESS/IVG co,1/rRoLz.e-R I S/GNAL FROM SP/RL CONTROLLER CONCENTRA TE CONCEN TRA TE T0 l Ilm PRom/cr 0R FURTHER u MHH uu/pfmcsss/.NG

CUNCENTRATE /V VENT-0l?. RETURNED T0 LUTHER 6. HENDR/CKSON United States Patent Gliiice 3,235,0l79 Patented Feb. l5, 19%6 3,235,079 METHD AND APPARATUS FR CNTROLLING SilRAL CONCENTRATORS Luther G. Hendrickson, Duluth, Minn., assignor to United States Steel Corporation, a corporation of Delaware Filed .luly 10, 1962, Ser. No. 208,757 7 Claims. (Cl. 209-459) This invention relates to an improved method and apparatus for controlling flow of materials in a spiral concentrating plant.

Conventionally a spiral concentrating plant has a large bank of parallel rougher spirals and a smaller bank of parallel cleaner spirals. Each spiral includes a helical trough and a vertical collecting pipe which extends along the axis of the helix. A pulp of water and nely divided solids (for example minus 50 mesh iron ore) is introduced from a distributor to the upper ends of the rougher spirals. As the pulp flows down the trough of each spiral, heavier particles among the solids remain nearer the axis of the helix and lighter particles move toward the outside. Wash water is introduced to the pulp stream as it iiows down the trough to wash away lighter particles and thus improve the separation. The trough has concentrate collection ports near its inner edge through which heavier particles discharge into the collecting pipe. These ports are equipped with cutters whose position can be adjusted to regulate the width of stream routed to the concentrate. Intermediate and lower density particles discharge separately at the bottom of the trough. Thus rougher spirals separate solids in the pulp into Concentrate, middlings and tailings. The rougher concentrate usually goes to the cleaner spirals, which act on it in like manner to produce a final concentrate. For a more detailed description of a spiral concentrator, reference may be made to printed publications by Taggart, Handbook of Mineral Dressing, copyright 1945, page l1- 135, or Elements of Ore Dressing, copyright 1951, page 212, both published by lohn Wiley and Sons, Inc., New York.

For spiral concentrators to operate properly, each spiral in a bank should receive a relatively Constant weight of solids, and the pulp reaching the spirals should have a relatively constant solids-to-water ratio or density. In practice feed rates often fluctuate. An increase in the feed rate tends to lower the recovery, while a decrease tends to lower the grade of concentrate. Some compensation is possible by adjusting the wash water rate. For extreme variations it is sometimes necessary to adjust positions of cutters in the concentrate collection ports. This is an extremely time consuming procedure and should be avoided. Adjustment is also possible by manually cutting individual spirals into and out of operation, but the amount of correction is limited unless a variable speed pump is used.

An object of my invention is to provide an improved control method and apparatus, applicable particularly to cleaner spirals, for automatically maintaining both the weight of solids feeding to each spiral and the solidsto water ratio of the feed at constant values, and in which all spirals in a bank remains in continuous operation.

A further object is to provide an improved control method and apparatus which utilize a constant speed pump for feeding pulp to all the spirals of a bank, and an automatically adjustable splitter for returning a variable portion of the concentrate from the spirals to the pump for recycling as required to maintain constant conditions in the spirals.

A further object is to provide an improved method and apparatus for controlling flow of material in a spiral plant in which automatic adjustments are made both in the volume of water added to an ore pulp and in the proportion of concentrate returning to the pump for recycling to maintain the pulp at a relatively constant density, and in which the weight of solids in each spiral is maintained constant by use of a constant volume pump.

A further object is to provide a method and apparatus for automatically controlling a spiral concentrating circuit in which a portion of the concentrate is continuously recycled, thereby upgrading the product, as well as utilizing capacity otherwise idle.

A further object is to provide an improved splitter for dividing a stream of material into variable fractions.

In the drawing:

FIGURE l is a schematic tiowsheet of my improved control method and apparatus; and

FIGURE 2 is a perspective view of the improved splitter embodied in my apparatus.

F lowsheet FIGURE l shows a ilowsheet of a spiral concentrating plant which includes a pump box i0, a constant speed pump 12, a spiral feed distributor 13, and a bank of individual parallel spiral concentrators i4, 14a, Mb, 14e, etc. lf the spirals are used as cleaners, the original feed (for example a pulp of water and minus 50 mesh iron ore) commonly is a concentrate product from rougher spirals (not shown). This feed enters the pump box lil, from which pump I2 withdraws it at constant volume and transfers it through a line l5 to the distributor i3. From there lines 16, 16a, etc. carry equal shares of the pulp to the individual spirals, which separate solids therein into concentrate and tailing products. The individual pieces of apparatus and the portion of the tlowsheet thus far described are conventional and hence not described in greater detail. Although the flowshcet shows only four spirals, a spiral bank in a commercial plant ordinarily has a much larger number (for example forty to fifty cleaner spirals or about twice as many rougher spirals).

As the tlowsheet also shows, water is introduced to the pump box it) through a line 17 to dilute the pulp. As also known in the art, the pump box is equipped with mechanism for maintaining a substantially Constant level of diluted pulp therein. This mechanism includes a level senser and controller i3 connected with the pump box, a valve positioner i9 operatively connected with the controller, and an adjustable valve Ztl in the water line 17 leading to the pump box. The valve positioner automatically adjusts the valve to admit water in the volume needed to maintain a constant level in the pump box.

In accordance with my invention, I collect the concentrate products from spirals 1d, Ma, etc. in a line 21. This line leads to a splitter Z2, which intercepts a portion oi the concentrate product and returns it via a line 23 to the pump box 10. The returned concentrate is recycled through the spirals along with the original feed. The position of the splitter is adjustable to vary the proportion of concentrate which returns in this manner. I connect a positioner 24 to the splitter for propelling it to its diierent positions of adjustment. I mount a pulp density meter 2S in line 115' which leads from pump l2 to distributor 13. I connect the pulp density meter to a recorder-controller 26, and connect the latter to the positioner. Thus the positioner automatically moves the splitter to maintain control. The portion of the pulp stream intercepted varies inversely with changes in the pulp density.

Splitter FlGURE 2 shows structural details of my preferred form of splitter 22. Line 2l from the spirals terminates in a rst fixed launder 21a. A second fixed launder 23a is located beneath launder 21a to receive concen.

trate returning via line 23. A third fixed launder 29 is located beneath launder 23a and offset therefrom to receive the portion of the concentrate not returning but leaving as a final product of the circuit. The splitter includes a swinging launder 30 and a pair of links 31 attached to this launder and pivoted to an overhead support 3?.. The swinging launder is located in the space between the fixed launders 21a and 23a and it has an outlet spout 33 in its end above the fixed launder 29. The positioner 24 is connected to the links 31 to move the swinging launder back and forth in response to signals from the recorder-controller 26.

Instruments The individual instruments used in my control ap paratus are of conventional construction and available commercially. Hence I have not shown nor described them in detail, but instead reference can be made to printed publications for showings. Considine, Process Instruments and Controls Handbook published by Mc- Graw Hill Book Company, copyright 1957, Library of Congress Catalog7 Card No. 56-8169 shows and describes instruments suitable for most of my purposes. Considine shows a bubbler (page -23) and a force balance unit (page 548) of types suitable for my level senser and controller 1S, and also a diaphragm motor (page 10-32) of a type suitable for my valve positioner 19. A suitable force unit and water valve also are available commercially from Fisher Governor Co. Marshalltown, Iowa, as types Z500-2419? and 657AR respectively. This particular force balance unit gives an output signal which varies from 3 to 15 p.s.i.g. and is sufficient to operate the valve motor directly. Considine shows a cylinder-type operator with positioner (page lO-37), a recorder (page 8-109), and controller (proportional-pilus-reset, page 11-22, or proportionalplus-reset-plus-rate, page 1l-26) suitable for my positioner 22% and my recorder-controller 26. A suitable recorder-controller also is available commercially from Leeds and Northrup Company, Philadelphia, Pa., as type H with a type CAT controller. This controller transmits electric signals to an electric-to-pneumatic converter, such as Fisher Governor CO. type 543. A suitable positioner is available commercially from Foxboro Company, Foxboro, Mass., as the Stabiload The pneumatic signal from the transducer positions the latter device proportionally to the magnitude of signal to locate the splitter in the proper place. The pulp density meter can be an Ohmart cell as shown in Ohmart Patent No. 2,763,790.

Operation To describe the way my control operates, I assume initially the flow of materials is stabilized with splitter .22 returning a definite volume of pulp to pump box 10. Pump 12 continuously withdraws a constant volume of pulp from the pump box. This pulp is replaced continuously by an equal volume of pulp made up of (a) new pulp feeding to the pump box, (b) concentrate returning to the pump box via line 23, and (c) water introduced via line 17. Now I assume the feed rate of new solids to the pump box 1G diminishes. The level of material in the pump box starts to drop, but the level sensing device 18 detects the drop, whereupon the valve positioner 19 adjusts valve 20 to admit a greater volume of water to the pump box. The level of material is restored, but the pulp is more dilute. The pulp density meter detects a decrease in density, whereupon the recorder-controller 26 actuates the splitter positioner 24 to shift the splitter 22 in a direction to return a greater quantity of concentrate to the pump box. Now the level of material in the pump box commences to rise, whereupon valve 20 is adjusted to admit a smaller volume of water. The larger proportion of returning concentrate raises the density counter to the effect of water introduced through line I7. The foregoing action is repeated periodically until the density is restored to its set value and the flow of materials again is stabilized. The reverse action of course takes place when the weight of new solids in the feed increases. Since the pump delivers material at constant volume and the control apparatus maintains a constant density, the weight of solids in each spiral necessarily remains constant. In the example of iron ore, the pulp typically has a solids content of about 25 to 40 percent by Weight, but for any particular ore the content is held as nearly constant as possible.

From the foregoing description it is seen that my invention affords a dependable automatic method and apparatus for controlling flow of water and solids in a spiral concentrating plant. All spirals operate at all times, and any excess capacity is used advantageously for recycling the concentrate product, and thus upgrading it. If there is a decrease in heavy mineral content of rougher feed, the rougher concentrate is often of lower grade, as well as smaller in quantity. When my invention is applied to a bank of cleaner spirals, it offers a special advantage that a smaller quantity of rougher concentrate automatically leads to a greater re-circulation of cleaner concentrate. Thus a larger part of the lower grade feed is cleaned twice. The invention utilizes only control instruments which are available commercially. Consequently the apparatus is readily assembled and applied to existing plants.

While I have shown and described only a single ernbodiment of my invention, it is apparent that modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. In a concentrating process in which a pulp of water and finely divided solids feeds into a pump box, additional water is introduced to the pump box to dilute the pulp and thereby decrease its density, the volume of the additional water is regulated to maintain a substantially constant level of the diluted pulp in the pump box, a pump transfers the diluted pulp at constant volume to a bank of parallel spiral concentrators, and the concentrators separate solids in the pulp into concentrate and tailing products, the combination therewith of a control method comprising measuring the density of the diluted pulp before it reaches said concentrators generating a signal representative of the density measurement, returning to said pump box a portion of the concentrate product from said concentrators to counter the decrease in density of the pulp in said box brought about by the additional water, and varying the portion of returning concentrate in response to changes in said signal to maintain the diluted pulp at a relatively constant density, a relatively constant weight of solids in each conccntrator, and all concentrators in the bank in continuous operation.

2. In a concentrating process in which a pulp of water and finely divided solids feeds into a pump box, additional Water is introduced to the pump box to dilute the pulp and thereby decreased its density, the volume of the additional water is regulated to maintain a substantially constant level of diluted pulp in the pump box, a pump transfers the diluted pulp at constant volume to a distributor, the pulp goes from the distributor to a bank of parallel spiral concentrators in equal shares to the individual concentrators, and the concentrators separate solids in the pulp into concentrate and tailing products, the combination therewith of a control method comprising measuring the density of the diluted pulp before it reaches said concentrators, intercepting a portion of thc concentrate product from said concentrators, varying the portion intercepted inversely with changes in the density measurement, and returning the intercepted portion to the pump box to counter the decrease in density of the pulp in said box brought about by the additional water,

thereby maintaining the pulp in the concentrators at a relatively constant density, maintaining a relatively constant weight of solids in each concentrator, and maintaining all concentrators in the bank in continuous operation.

3. In a concentrating process in which a pulp of water and finely divided solids feeds into a pump box, additional water is introduced to the pump box to dilute the pulp and thereby decrease its density, the volume of the additional water is regulated to maintain a substantially constant level of diluted pulp in the pump box, a pump transfers the diluted pulp at constant volume to a distributor, the pulp goes from the distributor to a bank of parallel spiral concentrators in equal shares to the individual concentrators, and the concentrators separate solids in the pulp into concentrate and tailing products, the combination therewith of a control method comprising measuring the density of the diluted pulp before it reaches said concentrators, intercepting a portion of the concentrate product from said concentrators, varying the portion intercepted inversely with changes in the density measure ment, returning the intercepted portion to the pump box to counter the decrease in density of the pulp in said box brought about by the additional water, and recycling the intercepted portion through the concentrators to subject it to `further separation, thereby maintaining the pulp in the concentrators at a relatively constant density, maintaining a relatively constant weight of solids in each concentrator, and maintaining all concentrators in the bank in continuous operation.

4. A method as delined in claim 3 in which the concentrators are cleaners and the solids in the feed are a concentrate product from rougher spiral concentrators.

5. In a concentrating plant which includes a pump box, means for feeding a pulp of water and iinely divided solids to said pump box, means for introducing additional water to said pump box to dilute the pulp and thereby decrease its density, means regulating the volume of additional water introduced to said pump box to maintain a substantially constant -level of diluted pulp therein, a constant speed pump for withdrawing pulp at constant volume from said pump box, a distributor, a bank of parallel spiral concentrators, lines leading from said pump to said distributor and thence to said concentrators, and means for collecting concentrate from said concentrators, the combination therewith of a control apparatus comprising means for measuring the density of the diluted pulp and generating a signal representative thereof, means for intercepting a portion of the concentrate from said collecting means, means operatively connected with said signal-generating means and with said intercepting means for varying the proportion of concentrate intercepted inversely with changes in the density measurement, and means returning the intercepted concentrate to said pump box to counter the decrease in density of the pulp in said box brought about by the additional water, thereby maintaining the pulp in the concentrators at a relatively constant density, maintaining a relatively constant weight of solids in each concentrator, and maintaining all concentrators in the bank in continuous operation.

6. In a concentrating plant which includes a pump box, means for feeding a pulp of water and linely divided solids to said pump box, means for introducing additional water to said pump box to dilute the pulp and thereby decrease its density, means regulating the volume of :additional CII water introduced to said pump box to maintain a substantially constant level of diluted pulp therein, a constant speed pump for withdrawing pulp at constant volume from said pump box, a distributor, a bank of parallel spiral concentrators, lines leading from said pump to said distributor and thence to said concentrators, and means for collecting concentrate from said concentrators, the combination therewith of a control vapparatus comprising means operatively connected with the line leading from said pump for measuring the density of the diluted pulp and generating a signal representative thereof, a splitter in said collecting means for intercepting a portion of the concentrate, means operatively connected with said signalgenerating means and with said splitter for varying the proportion of concentrate intercepted inversely with changes in the density measurement, and means returning the intercepted concentrate to said pump box to counter the decrease in density of the pulp in said box brought about by the additional water, thereby maintaining the pulp in the concentrators at a relatively constant density, maintaining a relatively constant weight of solids in each concentrator, and maintaining all concentrators in the bank in continuous operation.

7. In a concentrating plant which includes a pump box, means for feeding a pulp of water and nely divided solids to said pump box, means for introducing additional water to said pump box to dilute the pulp and thereby decrease its density, means regulating the volume of additional water introduced to said pump box to maintain a substantially constant level of diluted pulp therein, a constant speed pump for withdrawing pulp at constant volume from said pump box, a distributor, a bank of parallel spiral concentrators, lines leading from said pump to said distributor and thence to said concentrators, and means for collecting concentrate from said concentrators, the combination therewith of a control apparatus comprising a pulp density meter operatively connected with the line leading from said pump for generating a signal representative of the density of pulp leaving said pump, an adjustable splitter in said collecting means for intercepting a portion of the concentrate, which portion varies in magnitude with the position of the splitter, means operatively connected with said signal-generating means and with said splitter for adjusting the position of said splitter to vary the proportion of concentrate intercepted inversely with density changes, and means returning the intercepted concentrate to said pump box to counter the decrease in density of the pulp in said box brought about by the additional water, thereby maintaining the pulp in the concentrators at a relatively constant density, maintaining a relatively constant Weight of solids in each concentrator, and maintaining all concentrators in the bank in continuous operation.

References Cited by the Examiner UNITED STATES PATENTS 2,431,559 11/ 1947 Humphreys 209-211 2,626,635 1/1953 Eckstein 137-610 3,006,367 10/ 1961 Thompson 137-610 3,099,621 8/ 1963 Close 209-459 HARRY B. THORNTON, Primary Examiner. FRANK W. LUTTER, Examiner. 

1. IN A CONCENTRATING PROCESS IN WHICH A PULP OF WATER AND FINELY DIVIDED SOLIDS FEEDS INTO A PUMP BOX, ADDITIONAL WATER IS INTRODUCED TO THE PUMP BOX TO DILUTE THE PULP AND THEREBY DECREASE ITS DENSITY, THE VOLUME OF THE ADDITIONAL WATER IS REGULATED TO MAINTAIN A SUBSTANTIALLY CONSTANT LEVEL OF THE DILUTED PULP IN THE PUMP BOX, A PUMP TRANSFERS THE DILUTED PULP AT CONSTANT VOLUME TO A BANK OF PARALLEL SPIRAL CONCENTRATORS, AND THE CONCENTRATOROS SEPARATE SOLIDS IN THE PULP INTO CONCENTRATE AND TAILING PRODUCTS, THE COMBINATION THEREWITH OF A CONTROL METHOD COMPRISING MEASURING THE DENSITY OF THE DILUTED PULP BEFORE IT REACHES SAID CONCENTRATORS GENERATING A SIGNAL REPRESENTATIVE OF THE DENSITY MEASUREMENT, RETURNING TO SAID PUMP BOX A PORTION OF THE CONCENTRATE PRODUCT FROM SAID CONCENTRATORS TO COUNTER THE DECREASE IN DENSITY OF THE PULP IN SAID BOX BROUGHT ABOUT BY THE ADDITIONAL WATER, AND VARYING THE PORTION OF RETURNING CONCENTRATE IN RESPONSE TO CHANGES IN SAID SIGNAL TO MAINTAIN THE DILUTED PULP AT A RELATIVELY CONSTANT DENSITY, A RELATIVELY CONSTANT WEIGHT OF SOLIDS IN EACH CONCENTRATOR, AND ALL CONCENTRATORS IN THE BANK IN CONTINUOUS OPERATION. 